Results from the Children's Health Study (CHS) indicate that chronic exposure to a package of combustion-related ambient air pollutants (nitrogen dioxide, NO2; respirable particulate matter, PM10 and PM2.5; and vapor acids) decrease the rate of lung function growth and increase the frequency and severity of childhood respiratory illnesses. The researchers propose to investigate 3 new research questions: (1) Do the childhood deficits in lung function growth rates associated with exposure to elevated levels of N02, acids, and respirable particles persist and result in lower maximum lung function at maturity; (2) Are specific components of motor vehicle exhaust responsible for the chronic effects of ambient combustion-derived air pollution on children?s lung function or respiratory illnesses ultra-fine particle (less than O.1 microns, um) number concentration, fine particle (less than 2.5 um) metals, fine diesel exhaust particles (EC), polycyclic aromatic hydrocarbons (PAHs)/aldehydes/ketones/quinones, freshly emitted vehicle exhaust (carbon monoxide, CO; and other models); and (3) Are subgroups of children more susceptible to adverse respiratory effects of ambient combustion-derived air pollutants? These research questions will be investigated by accomplishing the following specific aims: (1) locating 1,500 former CHS participants who have reached maturity, measuring maximum lung function at their homes, and assessing lifetime exposure to ozone (03), NO2, and PM10; (2) measuring lung function growth while concurrently assessing exposure to ultra-fine particle number concentration, fine particle metals, EC, PAHs, and CO for 3 years in the 1,200 CHS participants still in high school; and (3) examining the influences of host factors such as gender, genetics and nutritional factors in modifying the effects. These new data, combined with the extensive CHS database, offer a unique opportunity to refine knowledge of the chronic effects of combustion-derived air pollutants and to provide data to improve regulatory strategies.